The present invention relates generally to the stabilization or immobilization of vertebral bodies in the spinal column, as well as methods and instruments for achieving same.
The spinal column of humans provides support for the body and protection to the delicate spinal cord and nerves. The spinal column comprises a series of vertebrae stacked on top of each other. Each vertebra has a relatively large vertebral body located in the anterior portion of the spine and provides the majority of the weight bearing support of the vertebral column. Each vertebral body has relatively strong bone comprising the outside surface of the body (cortical) and relatively weak bone comprising the center of the body (cancellous). Situated between each vertebral body is an intervertebral disc, which provides for cushioning and dampening of compressive forces to the spinal column. Located just posterior to the vertebral body and intervertebral disc is the vertebral canal containing the delicate spinal cord and nerves. Posterior to the spinal canal are the different articulating processes of the vertebra.
Various types of spinal column disorders are known and include scoliosis (abnormal lateral curvature of the spine), kyphosis (abnormal forward curvature of the spine, usually in the thoracic spine), excess lordosis (abnormal backward curvature of the spine, usually in the lumbar spine), spondylolisthesis (forward displacement of one vertebra over another, usually in a lumbar or cervical spine) and other disorders caused by abnormalities, disease or trauma, such as ruptured or slipped discs, degenerative disc disease, fractured vertebra, and the like. Patients that suffer from such conditions usually experience extreme and debilitating pain and often neurologic deficit.
Spinal fusion is a technique often utilizing surgical implants which mechanically immobilize areas of the spine with eventual incorporation of grafting material. Such techniques have been used effectively to treat the above-described conditions and, in most cases, to relieve pain suffered by the patient. However, there are some disadvantages to the present fixation devices.
One technique for spinal fixation includes immobilization of the spine by the use of spine rods that run generally parallel to the spine. In practicing this technique, the posterior surface of the spine is exposed, and bone screws are first fastened to the pedicles of the appropriate vertebrae or to the sacrum, acting as anchor points for the spine rods. The bone screws are generally placed two per vertebrae, one at each pedicle on either side of the spinous process. Clamp assemblies join the spine rods to the screws. The spine rods are generally bent to achieve the desired curvature of the spinal column. Such systems are very stable but require implanting screws into each vertebrae to be treated. Also, since the pedicles of vertebrae above the second lumbar vertebra (L2) are very small, only small bone screws can be used, which sometimes do not give the needed support to stabilize the spine. To stabilize the unstable spine sufficiently, one to two vertebrae above and one to two vertebrae below the area to be treated are often used for implanting the screws. The rods and clamps are surgically fixed to the spine from a posterior approach.
Anterior fixation devices have also been used, such as anterior plate systems. One type of anterior plate system involves a titanium plate with unicortical titanium bone screws that lock to the plate and are placed over the anterior surface of the vertebral body. Another type of anterolateral plate system used less frequently involves the use of bicortical screws that do not lock to the plate. The bone screws have to be long enough to bite into both sides of the vertebral body to gain enough strength to obtain the needed stability. These devices are difficult to place due to the length of the screws, and damage occurs when the screws are misplaced.
A third type of anterior fixation device comprises a hollow device that may or may not be externally threaded. The device is positioned between two adjacent vertebral bodies. Bone grafts from cadavers or from the pelvic region of the patient may be placed into the hollow center of the device. Bone morphogenic protein or other substances that promote bone growth can also be placed into the hollow center of the device. The cage might allow bone to grow through the device and fuse the two adjacent vertebrae.
Although the devices described above present various solutions, further improvement in this area is desirable. There remains a need to have a stabilization device which connects to the strong vertebral bodies. The device should be easy to place and should prevent potentially damaging telescoping of adjacent vertebrae.
The present invention overcomes the drawbacks in the prior art by providing a stabilization device having greater intrinsic stability. The present invention also overcomes drawbacks associated with the prior art by providing a stabilization device which can restore the proper height between adjacent vertebrae in one implant. Moreover, the stabilization device of the present invention may provide a greater area of space for bone grafts.
One aspect of the present invention provides a stabilization device. The stabilization device includes a plate adapted for fixation to the sides of adjacent vertebral bodies. The device also includes at least two legs attached to the plate which are adapted for disposal between the adjacent vertebral bodies to provide support therebetween. There is a space between two of the legs such that together with the plate a U shape is formed as viewed superior to inferior. Preferably, the legs extend along the plane which is transverse to the plane of the plate. More preferably, the legs extend along a plane which is substantially perpendicular to the plane of the plate.
Another aspect of the present invention provides a method of stabilizing adjacent vertebral bodies. The method includes the steps of: providing a stabilization device having at least two legs and a bridging member connecting the legs to define an approximate U-shape as viewed superior to inferior; inserting the stabilization device between the adjacent vertebral bodies such that the legs extend in a direction between anterior and posterior; and fixing the stabilization device by inserting at least one fixation device into the anterior or posterior face of at least one of the adjacent vertebral bodies. Preferably, the method also includes the step of inserting a fixation member along the legs. In a more preferred embodiment, the legs may include a recess extending in a direction between anterior and posterior. The method may further include the step of inserting a leg fixation member within the recess such that the leg fixation member is partly in at least one of the adjacent vertebral bodies and partly in the recess along the axis of said leg.
In yet another aspect of the invention, a stabilization device is provided that includes an intervertebral body adapted for positioning between adjacent vertebral bodies. The intervertebral body has a first end and a second end, and a first surface and a second surface for contacting the respective surfaces of the vertebral bodies. The stabilization device also includes a fixation member adapted to fix the intervertebral body to one of the adjacent vertebral bodies. The fixation member is sized so that when positioned for fixation, a portion of the member extends beyond the first surface of the intervertebral body and engages the bone of the vertebral body. In a preferred embodiment, no portion of the fixation member extends beyond the second surface of the intervertebral body.
In preferred embodiments, the stabilization device may also include a channel formed in at least one of the first and second surfaces of the intervertebral body. The channel may extend between the first and second ends of the intervertebral body. In a more preferred embodiment, the stabilization device may further include a fixation member having a width, which when positioned for fixation, is partially in one of the vertebral bodies, the remaining portion being exterior to the vertebral bodies, preferably within the intervertebral body. Preferably, at least about 25% of the width of the fixation member is in one of the vertebral bodies. Most preferably, when positioned for fixation, about 25% to about 50% of the width of the fixation member is in one of the vertebral bodies. Of course, the fixation member can be in one of the vertebral bodies outside of this range.
In an alternative embodiment, the stabilization device may include a plate attached to the intervertebral body. The plate may be adapted for fixation to the anterior, lateral or posterior sides of at least one of the adjacent vertebral bodies. In a preferred embodiment, the plate is adapted for fixation to the anterior or lateral sides of both of the adjacent vertebral bodies. In a most preferred embodiment, the plate is adapted for fixation the anterior side of both of the adjacent vertebral bodies.
In a further aspect of the invention, a method is provided for stabilizing adjacent vertebral bodies. The method includes inserting an intervertebral body between the adjacent vertebral bodies. The intervertebral body has a first end and a second end, and a first surface and a second surface, which contact the respective surfaces of the vertebral bodies. The method also includes inserting at least one fixation member which is sized so that a portion of the fixation member extends beyond the first surface of the intervertebral body and engages the bone of one of the vertebral bodies. In a preferred embodiment, no portion of the fixation member extends beyond the second surface of the intervertebral body. More preferably, when the fixation member is positioned for fixation, the fixation member is partially in one of the vertebral bodies, the remaining portion being exterior to the vertebral bodies, preferably within the intervertebral body. Preferably, at least about 25% of the width of the fixation member is in one of the vertebral bodies. Most preferably, about 25% to about 50% of the width of said fixation member is in one of the vertebral bodies and the remaining width of said fixation member is within said intervertebral body. Of course, the fixation member can be in one of the vertebral bodies outside of this range.
In a preferred embodiment, the method may also include inserting an intervertebral body having a channel formed in at least one of the first and second surfaces. The channel may extend between the first and second ends of the intervertebral body.
In another preferred embodiment, the method further includes the step of affixing a plate, which is attached to the intervertebral body, to the anterior, lateral or posterior side of at least one of the adjacent vertebral bodies. More preferably, the plate is affixed to the anterior or lateral sides of both of the adjacent vertebral bodies. Most preferably, the plate is affixed to the anterior side of both of the adjacent vertebral bodies.
A further aspect of the invention provides a stabilization device that includes an intervertebral body adapted for positioning between adjacent vertebral bodies. The intervertebral body has a first end and a second end, and a first surface and a second surface for contacting the respective surfaces of the vertebral bodies. The intervertebral body is constructed and arranged to allow the stabilization device to flex superiorly and inferiorly when arranged between the vertebral bodies and prior to fusion of the vertebral bodies. In a preferred embodiment, the stabilization device includes a slot extending transversely in a direction between anterior and posterior to allow the stabilization device to flex superiorly and inferiorly when arranged between the vertebral bodies and prior to fusion of the vertebral bodies.
In an alternative embodiment, the stabilization device may include a plate adapted for fixation to the anterior, lateral or posterior sides of the adjacent vertebral bodies. The device may also include legs extending transversely from the plate such that there is a space between the legs. The legs extend with the sides of said plate to form an approximate U-shaped device. The legs may also include a slot extending transversely in a direction between anterior and posterior to allow the stabilization device to flex superiorly and inferiorly when arranged between the vertebral bodies and prior to fusion of the vertebral bodies.
In another alternative embodiment, the device may include a plate adapted for fixation to the anterior, lateral or posterior sides of the adjacent vertebral bodies. The device may further include legs extending transversely from the plate such that there is a space between the legs. The legs may extend with the sides of the plate to form an approximate U-shaped device. Further, the legs may be of different elasticity than the plate to allow the stabilization device to flex superiorly and inferiorly when arranged between the vertebral bodies and prior to fusion of the vertebral bodies. In a preferred embodiment, the legs are formed from polyethylene ether ketone (PEEK).
In yet a further aspect of the invention, a method is provided for stabilizing adjacent vertebral bodies. This method includes the step of inserting a stabilization device between adjacent vertebral bodies. The stabilization device has a first end and a second end, and a first surface and a second surface for contacting the respective surfaces of the vertebral bodies. The stabilization device is constructed and arranged to allow the stabilization device to flex superiorly and inferiorly when arranged between the vertebral bodies and prior to fusion of the vertebral bodies. In a preferred embodiment, the method may include inserting a stabilization device having a slot extending transversely in a direction between anterior and posterior to allow the stabilization device to flex superiorly and inferiorly when arranged between the vertebral bodies and prior to fusion of the vertebral bodies. In certain preferred embodiments, the method may include inserting a stabilization device that has a plate adapted for fixation to the anterior, lateral or posterior sides of adjacent vertebral bodies. The legs may extend transversely from the plate such that there is a space between the legs. The legs may also extend with the sides of the plate to form an approximate U-shaped device. In addition, the legs may include a slot extending transversely in a direction between anterior and posterior to allow the stabilization device to flex superiorly and inferiorly when arranged between the vertebral bodies and prior to fusion of the vertebral bodies.
In an alternative embodiment, the legs are of different elasticity than the plate to allow the stabilization device to flex superiorly and inferiorly when arranged between the vertebral bodies and prior to fusion of the vertebral bodies. In a preferred embodiment, the legs are formed from polyether ether ketone (PEEK).
A further aspect of the invention provides a modular stabilization device. The device includes a plate adapted for fixation to the anterior, lateral or posterior sides of adjacent vertebral bodies. The plate has a front face and a back face. The device also includes a separate stabilization member that has a first surface and a second surface for contacting the respective surfaces of the vertebral bodies. When the separate stabilization member is affixed to the back face of the plate, it extends along a plane which is substantially perpendicular to the plane of the plate.
A further aspect of the invention provides a method for reducing a displaced vertebra in the spine. The method includes providing a stabilization device having a plate adapted for fixation to the sides of adjacent vertebral bodies. The legs are adapted for disposal between the adjacent vertebral bodies to provide support therebetween. There is a space between the legs such that the legs and the plate together define an approximate U-shape as viewed superior to inferior. The stabilization device is positioned between a first vertebral body, which is in proper alignment with the remaining vertebral bodies, and a second vertebral body, which is not in proper alignment with the remaining vertebral bodies. The device is attached to the first vertebral body. The second vertebral body is then reduced by translating the second vertebral body so that it is in alignment with the first vertebral body. Finally, the device is attached to the second vertebral body.
In another aspect of the invention, a kit is provided that includes at least one plate adapted for fixation to the anterior, lateral or posterior sides of adjacent vertebral bodies. The plate has a front face and a back face, and a plurality of separate and different stabilization members attachable to the plate. The stabilization members have a first surface and a second surface for contacting the respective surfaces of the vertebral bodies, which when affixed to the back face of said plate extends along a plane which is transverse to the plane of the plate.
Alternatively the kit may include a plurality of separate and different plates adapted for fixation to the anterior, lateral or posterior sides of adjacent vertebral bodies, said plates having a front face and a back face, and at least one stabilization member having a first surface and a second surface for contacting the respective surfaces of the vertebral bodies, which when affixed to the back face of the plate extends along a plane which is transverse to the plane of the plate.
In an alternative embodiment, the kit may include multiple sized and shaped plates and stabilization members.
In yet another aspect of the invention, an apparatus is provided for use in manipulating a displaced vertebra in the spine. The apparatus includes a first extendable member for manipulating at least one vertebra, and a second extendable member cooperating with the first extendable member for manipulating at least one adjacent vertebra. Alternatively, the apparatus may also include a third extendable member which is slidably positioned between the first and second extendable members for distracting the adjacent vertebrae.